Nature Is Not Naturally Accommodating

Many trees naturally exhibit irregular form.

Gardening is quite unnatural. It involves unnatural cultivation of mostly unnaturally exotic (nonnative) species of plants. Irrigation delivers more water than seasonal rain provides. Fertilizers contribute more nutrients than endemic soils provide. Pesticides, if necessary, inhibit proliferation of pathogens. Nature simply could not accommodate such demands.

Not only is gardening unnatural, but it also interferes with established ecosystems. Many aggressively invasive plants were formerly desirable exotic plants that naturalized. Many pathogens arrived with exotic plants. Several naturalized plants have potential to distract native pollinators from native plants that rely on their pollination. It is an ecological mess.

Nonetheless, it works. Gardening within the constraints of nature would be unproductive. Most residents of California inhabit chaparral or desert climates that originally sustained limited vegetation. Such limited vegetation sustained a very limited indigenous populace within relatively vast areas. Modern residential parcels would be completely inadequate.

That is the justification for gardening, whether for sustenance, or merely to beautify home environments. Unnatural breeding continues to improve performance of many useful and appealing plants. Unnatural horticultural techniques generate more desirable vegetation within confinement of urban gardens than would naturally inhabit a few acres in the wild.

Nature remains relevant though. All plants originated within nature somewhere. Besides their basic requirements, exotic plants prefer environmental conditions that are similar to those of their natural origin. Some tropical plants crave more warmth and humidity. Some plants prefer more winter chill. Most popular exotic plants rely on supplemental irrigation.

Physical characteristics of many plants necessitate special accommodations also. Roots of plants that naturally compete in dense jungles are likely to damage pavement. Without adequate pruning, native plants that naturally exploit burn cycles can become perilously combustible. Many vines naturally try to overwhelm nearby vegetation and infrastructure.

Not all weeds are unwelcome.

Unplanned acacias certainly put on a show when they bloom. It is not easy to dislike something so impressively colorful.

Even the best tended gardens get weeds. Most weeds, particularly annual and perennial weeds, meet a quick demise by getting pulled out or sprayed with herbicide. A few shrub and tree weeds though, are sometimes allowed to mature into functional members of the landscape.

Many sneak into the garden by growing within overgrown or otherwise concealing shrubbery, where they can hide long enough to get established. Others are left to grow because they are recognized as desirable plants. The main problems is that many end up in situations where they eventually become problematic.

Mexican fan palms are distinctive trees. Unfortunately, many grow below utility cables, because that is where birds drop the seed as they eat the fruit. Unlike other trees, palms can not be pruned around utility cables, so must be removed when they get too tall.

Silk tree, black locust, tree of Heaven and various oaks, pines, acacias and eucalypti are some of the more common trees that can sneak into gardens. Sometimes, they happen to land in good situations. More often though, they get too close to foundations, eaves, pavement or other features that they damage as they grow. Like Mexican fan palms, they are easier to remove while young, before they become problematic.

Pittosporums, cotoneasters and privets are commonly seeded shrubbery with less potential for problems. The main problem with glossy privet is that it can be too prolific and aggressive, so that it can crowd out more desirable plants. Most pittosporums and cotoneasters that get seeded are from plants that are ‘straight species’ (not cloned cultivars or varieties). Those that happen to be from cultivar or variety plants will not be ‘true to type’, which means that they will be more like the straight species than like their parents.

The few fruit trees that can sometimes grow from seed have the same problem, since only some of the more genetically basic types may resemble their parents. Fancier types and (non-sterile) hybrids probably will not. Fruit trees that grow from root suckers of grafted trees instead of from seed will be nothing like the parents, and may produce useless fruit.

Pampas grass is a prolific and sometimes welcome perennial weed near untended parcels or forested areas where pampas grass has naturalized. Broom is a shrubby weed that is even more prolific, but never welcome.

Algerian and English ivy rarely grow from seed, but can be really nasty weeds if they get where they are not wanted. Bear’s breech (or breaches), Jupiter’s beard, calla, mint and various yuccas that were planted may be very difficult to eradicate if they are no longer desirable, or if they migrate into areas where they become problematic.

Weeds Are Full Of Surprises

Pokeweed is rapidly becoming more common.

While it was busy naturalizing in Australia, South Africa and southern South America, the California poppy was getting forced out of parts of its own native range by more aggressive exotic plants that were also busy getting naturalized. Technically, any plant that is not native is exotic. Any exotic plant that becomes naturalized in a foreign environment is able to proliferate without any help, as if it were native. Naturalized exotic plants that get too aggressive become invasive weeds.

Weeds are plants where they are not wanted. This is a very broad definition that includes plants ranging from simple little dandelions in urban lawns to humongous bluegum eucalyptus in forests. Naturalized exotic weeds can be much more problematic than weeds that can only proliferate where they get watered in gardens and landscapes, because they can get established where they are not expected.

Water hyacinth that clogs the Sacramento and San Joaquin River Delta is not often a problem in terrestrial landscapes. However, giant reed, pampas grass, Acacia dealbata and blackberry brambles can infest home gardens just as easily as they infest wild lands. Because they do not need to be watered, they can get established and grow quite large in unused parts of the garden before anyone notices.

Many naturalized weeds somehow seem to much more aggressive and problematic than even the most prolific of native plants. Even the common native lupines are relatively docile compared to annual oat grass. Native blackberry may seem impossible to eradicate, but is actually neither as persistent nor as unpleasant to handle as the exotic Siberian blackberry!

Young weeds are easiest to pull now while the soil is still evenly damp, and young roots are only beginning to disperse. They will be more difficult to pull after roots are dispersed and soil hardens. Tree weeds and large perennial weeds that were cut down last year instead of pulled will likely need to be dug. Bermuda grass is a relatively low perennial grass that always seems to be difficult to dig. Mowing or cutting down annual grass weeds with a weed whacker will not eliminate them, but limits the development and dispersion of seed for the next generation. Burclover, sowthistle, bindweed, purslane, spurge and the various oxalis are some of the other common weeds that really get going this time of year.

Silver Wattle

Silver wattle is a magnificent weed.

Almost everyone on the West Coast of California has encountered silver wattle, Acacia dealbata. Some of us know how resilient it is to most methods of eradication. The more fortunate enjoy its magnificently bloom from a distance. It is almost never planted intentionally. It is an aggressively naturalized exotic species. Most grows wild near roadside ditches. Some invades home gardens.

The profuse and bright yellow bloom of silver wattle is spectacular while most deciduous trees remain bare late in winter. Big and billowy trusses of smaller round floral structures obscure most of their slightly grayish foliage. The many individual staminate flowers within this impressive bloom are actually minute. Their hearty floral fragrance is appealing to some, but objectionable to others.

Silver wattle lives fast and dies young. Some trees are so vigorous while young that they are unable to support their own weight. Without appropriate pruning, they simply fall over. Even stable and structurally sound trees deteriorate after about thirty years. Few survive for fifty. They seed prolifically though! Mature trees can get forty feet tall. The finely textured foliage is bipinnately compound.

Broom

00415
French broom seems to be indestructible.

Shortly after silver wattle finishes blooming up high, any of four species of broom begin blooming down low. Brooms and silver wattle often naturalize together. All bloom with the same delightfully brilliant yellow. The four brooms are French broom – Cytisus monspessulana, Scotch broom – Cytisus scoparius, Portuguese broom – Cytisus striatus and Spanish broom – Spartium junceum.

Sadly, none are desirable species. All are exotic weeds. They are only a topic for gardening because they are so aggressively invasive. Not only do they overwhelm and displace native species, but they also enhance soil nitrogen to promote the growth of other exotic weeds! They are unpalatable to deer, and are not bothered by insects or disease. Furthermore, brooms are combustible!

It is best to enjoy their cheery bloom from a distance, where they grow wild where they really should not. The various species tend to dominate distinct regions, with some degree of mingling. Big specimens can get eight feet tall, but do not live long as they are replaced by herds of seedlings. French broom is the only evergreen species; but any can defoliate in response to hot dry weather.

Wild Strawberry?

P00125K
Wild strawberries are worth salvaging.

Under a bank of carpet roses that I am none too keen on, this grubby ground cover competes with more aggressive weeds. To me, it looks like common mock strawberry, Potentilla indica. I never gave it much though. It seemed to me that whoever had installed cheap and common carpet roses on that bank would have employed a comparably cheap and common ground cover.

The ground cover was more prolific in open spots that were too narrow for more of the roses, and from there, seemed to have migrated under the roses as a second layer of ground cover. It would not have been installed underneath intentionally. It did not occur to me that it may have grown from seed like so many other weeds there, or migrated in from the surrounding forest.

The white flowers did catch my attention though. I was not aware of a mock strawberry that bloomed with white flowers. I really was not concerned enough about it to investigate. This part of the landscape will be getting renovated soon anyway. The roses will be relocated to where they can not extend their thorny canes into an adjacent walkway. Agapanthus will replace them.

Now that I am seeing more of these odd strawberries, I am wondering if this low ground cover that I formerly had no regard for is actually the native wild strawberry, Fragaria californica. Not only should mock strawberry bloom with yellow flowers, but it should also produce more spherical berries. Now I will need to identify it before I either dispose of it, or merely relocate it.

I prefer to not salvage exotic species that exhibit potential to naturalize from landscaped areas into surrounding forests. If this ground cover is wild strawberry, it migrated from surrounding forests into a particular casually landscaped area.

Mediterranean Climate Is Something Special

90925thumbThe climate here is pretty cool, at least in winter. Right now, it is pleasantly warm. It does not often get uncomfortably cold or hot, and when it does, it does not stay like that for too long. In between the warmest days of summer, the nights typically cool off nicely. In between the coolest nights of winter, the days typically warm up nicely. Humidity is normally minimal. Rain is adequate in season.

We have here what is known as a ‘Mediterranean’ climate. Obviously, it is similar to many climates of the Mediterranean Basin. Beyond the Mediterranean region, there are not many other places in the World that enjoy such reliably temperate weather. Most of such places are in southern and southwestern Australia, the Western Cape of South Africa, central Chile, and evidently, right here.

This particular region of Mediterranean climate is quite large, and extends into northern Baja California. Native plants know how to live here, and many of those that are adaptable to landscapes and home gardens can survive quite nicely with little or no irrigation. Some exotic (non-native) plants want climates with more warmth in summer, more chill in winter, or more rain through the year.

The best, as well as the worst, exotic plant species for local landscapes are those that are native to other Mediterranean climates.

The worst are those that are so happy in the local climate that they naturalize and become invasive to native ecosystems. Without pathogens or competing species that inhibited their proliferation within their respective native ranges, many naturalized species are detrimentally aggressive in ecosystems that they invade. Pampas grass, broom and Acacia dealbata are familiar examples.

The best exotics are not so threatening. Australian fuchsia, kangaroo paw, coprosma, westringia, bottle brush, grevillea, dracaena palm and eucalyptus originated from Australia. Lemon verbena, mayten and some salvias are from Chile. African iris, lily-of-the-Nile, bird-of-Paradise and all of the aloes came from South Africa. Olive, oleander, cistus, and all the lavenders are Mediterranean.

Like Peas In A Pod

P90622KGenerally, that is how they are. Almost all perennial pea flowers bloom with the same bright purplish pink color of the bloom in the picture below. That is, of course, before their pods develop, but you get the point. We sort of know what to expect from them.

As I mentioned in the ‘Six on Saturday‘ post last week, from which the picture below originated, variants like the pink bloom in the picture above are sometimes observed. The rare clear white flowers are my favorites. There might be fluffier double flowers too; although, in my opinion, the single flowers are prettier and look more like pea flowers should look.

I also mentioned last week that, although perennial pea has a sneaky way of growing where it is not wanted, it typically does not grow reliably from seed sown intentionally where it might actually be desirable. I have tried. The seed just did not cooperate. I managed to get a few to grow, but only because I put out a few hundred to compensate for the expected minimal rate of germination.

Because I like the white so much, I took seed from a vine that had bloomed with single white flowers. I figured that they would be more likely to produce a few white blooming progeny. I would have been satisfied if only a single vine in a group of several bloomed white, but got only a few vines that all bloomed with the typical bright purplish pink. They were pretty nonetheless, but were ironically removed when the site was redeveloped.

I also collected seed from vines that bloomed with the common single bright purplish pink flowers, just in case the viability rate of their seed might somehow be better. They were sown into a different situation, so even if I happened to know how many of the seed that were sown germinated and grew, it would not be an accurate comparison. Regardless, I was no more impressed with the result. Perennial pea is best appreciated as weed.P90615+++++

ICK!

P80915K.JPGJust about everything in this picture is icky! This species of pampas grass, Cortaderia jubata, is one of the most aggressive and noxious of the invasive exotic specie that have naturalized here. It seems to be incarcerated behind the weathered cyclone fence with barbed wire on top. The big water tank is is a harshly stark background. The tired old Douglas firs and ponderosa pines to the left and right seem to be unhappy here. The small coast live oak that is at least trying to make a more cheerful appearance is only oppressed by the surroundings. Only the clear blue sky above lacks the ick factor.

What is not visible in the picture is that there is no other flora in the area. Most of the area is covered with a thick layer of gravel to prevent vegetation from getting established close to the water tank. Weeds that manage to grow get cut down regularly. Only the pampas grass survives the ravages of the weed eater. It has been allowed to stay only because it has not yet been perceived to be a problem. It will probably be removed eventually as well. It would have been much easier to remove before it got so big. Now that it is blooming, it is likely to sow seed for more of the same.

Whomever gets the grim task of removing the pampas grass must contend with the nasty ‘razor grass’ foliage. The very sharp and very finely serrated edges of each leaf cause the worst sort of paper cuts! Even if handled very carefully, the long strap leaves have a way of getting everywhere. Someone tugging the base of the foliage with gloves and long sleeves can lose an ear to just one of the many long leaves that whip around so aimlessly.

However, someone who is unfamiliar with the serious nastiness of pampas grass might see this picture very differently. The firs, pines and oaks are not so bad. The water tank is a neutral background to the subject matter. The weathered cyclone fence with barbed wire on top, . . . well, let’s just say, . . . it’s ‘abstract’. Anyway, to someone who does not know better, the fluffy floral plumes of pampas grass that toss so many seed that have the potential to grow into an indefinite supply of the same nastiness are actually quite pretty.P89015K+.JPG

The Good Weed

P80616KOnce in a while, a stray seed of a plant that would normally be considered to be an invasive exotic species happens to grow in a spot where it happens to fit. Those of us who regularly pull up unwanted feral seedlings, are typically skeptical. We probably pull up many such seedlings merely because we do not trust them, or because we do not want them broadcasting their seeds elsewhere in the neighborhood. In our region, Acacia dealbata, blue gum eucalyptus, black locust, pampas grass, broom, poke berry and Himalayan blackberry get no consideration; and their seedlings should be removed as promptly as they are discovered. English ivy does not get much more consideration, but every once in a while, it happens to wander into a situation where it is allowed to stay.

Catalpa is one that we are not quite sure about. It is an exotic species that happens to disperse unwanted seed at times, but is not invasive enough to warrant prompt removal of all seedlings. Many seedlings appeared in the area several years ago, and most were removed because of where they were. However, if any other seedlings have appeared since then, they have been discreet enough to remain unnoticed. It was as if there was a very specific mating season. Catalpa had not been invasive prior to that, and has not been invasive since.

Two of the feral catalpa seedlings appeared on the edge of the parking lot at the Felton Presbyterian Church. One became disfigured and distressed, and finally died before being removed. The other just happened to be in the middle of a parkstrip, and in a location where a good sized shade tree had room to grow. Because no one could find a good reason for removal, it stayed. After only a few years, it is now a good sized and very well structured shade tree that blooms nicely this time of year. It may not last long, since catalpas are short lived, but for now, it is a nice component to the landscape. This weed gets a happy ending.